Leaves of plants that are used as food include Japanese parsley and cabbage, lettuce, spinach, Japanese radish leaves, tea leaves, and mulberry leaves. Among these, as a method of long-term storage of leafy vegetables such as Japanese parsley, cabbage, lettuce and spinach in the raw state, there is a method for storing them by putting them in a bag made of a film having a plurality of holes (see, for example, Japanese Patent Laid Open No. 6-199385). In addition, green tea leaves, oolong tea leaves and black tea leaves are generally stored in a dried state. In recent years, mulberry leaves, which had been primarily used in sericulture, are also produced as mulberry leaf tea (see, for example, Japanese Patent Laid Open No. 2006-101732) and stored by drying raw mulberry leaves after steaming them (see, for example, Japanese Patent Laid Open No. 9-206019).